1. Field of the Invention
The present invention relates to a communication apparatus for communicating between LANs through a wide area network or a communication apparatus for communicating with the traffic characteristics declared to the network before communication and, more particularly, to a communication apparatus for communicating at a traffic speed which corresponds to the amount of data transmitted.
2. Description of the Related Art
Communication between LANs
In order to interconnect distant LANs (Local Area Networks) with each other, a so-called wide area network (WAN) such as telephone network, data exchange network, ISDN and a leased line is inserted between the LANs. A router or a brouter is provided with functions of a bridge and a router is provided between each LAN and the WAN. In the communication system for connecting the LANs through a WAN, when a frame is sent from a terminal with a network address attached thereto, the router fetches the frame and transmits the frame to the LAN at the other end through the WAN by reference to the network address, the router connected to the LAN at the other end fetches the frame and transmits it to the LAN, and the terminal at the other end fetches the frame.
The band of the line in the WAN using the present public data network is so narrow that even in the communication between LANs, if the traffic is heavy, the transmission speed suddenly lowers to as low as 2400 bps, and even by using INS-C, which has a comparatively high speed, the transmission speed lowers to 64 Kbps. Therefore, a file transfer, which would be finished in several seconds within the same LAN, takes a much longer time through a WAN. Thus, the effective use of a WAN which enables the high-speed data transfer between LANs is an important problem which remains unsolved.
As an effective use of a line resource (network), a dynamic band assigning system is known, as described in the pending U.S. patent application Ser. No. 08/198,070 (application date: Feb. 17, 1994, Title: LAN-WAN-LAN COMMUNICATION METHOD AND APPARATUS FOR LAN-WAN CONNECTION). In this dynamic band assigning system, the traffic density is detected and the number of lines corresponding to the traffic density are assigned. In order to detect the traffic density in this system, the following method is adopted.
(1) The number of data remaining in the output buffer is counted, PA1 (2) the data dealt with are restricted to HDLC (High Level Data Link Control Procedure) and the number of frames is counted, or PA1 (3) the data dealt with are restricted to HDLC and the number of time fill flags are counted, and the traffic density is detected on the basis of the count value and, when the traffic density is high, the band is enlarged.
Such a dynamic band assigning system, however, suffers from the following problems. A first problem is that since the band is enlarged by increasing the number of channels or the like after the detection of the traffic density, it takes much time to secure the band. A second problem is that since whether or not there is a shortage of the bandwidth is only judged in the dynamic band assigning system, the appropriate band must be obtained by gradually enlarging the band by a predetermined amount, so that rapid and flexible assignment of band is sometimes impossible. A third problem is that a change in the transfer speed (band) during data transfer stops the transmission of data so as to establish synchronism, which is a problem in the reliability.
For example, if it is assumed that the band of 64 Kbps is assigned at present, in order to transmit data which requires a band of 384 Kbps, the traffic density is detected after the data transmission is started, and it is judged whether or not the band large enough for the traffic density is secured. If the band is too narrow, a channel is added so as to enlarge the band from 64 Kbps to 128 Kbps. However, if the band is still narrow, another channel is provided so as to enlarge the band from 128 Kbps to 192 Kbps. This operation is repeated so as to sequentially obtain the appropriate band. According to such a dynamic band assigning system, when the amount of traffic data is small and the transfer time is short, the desired band is not secured until the data transfer is almost finished, so that efficient data transfer is impossible.
In addition, although it is possible to select the method of setting the increment value of the band (in the above example, a method of setting the band to 320 Kbps at one time), but this method lacks in flexibility, so that the increment value is too large in another circumstance, and since it is impossible to set a band minutely, it is not practical from the point of view of economy.
ISDN communication/frame relay communication/ATM communication
In ISDN communication, frame relay communication and ATM communication, the originating terminal indicated the traffic characteristics (transfer speed (band), average speed, peak speed) to the network at calling. The network judges whether or not there is a path between the originating terminal and the terminating terminal which corresponds to the declared traffic characteristics. If there is such a path, the network connects these terminals through the path.
FIG. 17 is an explanatory view of the control procedure between the network and the user in the case of ISDN communication.
When the terminating terminal 2 is called by inputting a telephone number from the originating terminal 1 of a transmitter, a link is set between the originating terminal 1 and a network 3. When the link is set up, the originating terminal 1 supplies a SET UP message (call set-up request message) to the network 3. The network 3 transfers the SET UP message to the terminating terminal 2 and supplies a CALL PROC message to the originating terminal 1 to inform that the terminating terminal 2 is in the process of setting a call. When the processing for setting a call is finished, the terminating terminal 2 makes a ring tone and supplies an ALERT message (informing that the terminal 2 is being called) to the originating terminal 1 through the network 3. When a man answers the phone by taking up the receiver of the terminating terminal (off hook), the terminating terminal 2 sends a CONN message (informing that the phone is answered) to the network 3. The network 3 then sends a CONN ACK message (acknowledge) to the terminating terminal 2 and sends the CONN message to the originating terminal 1. When the originating terminal 1 receives the CONN message, it sends the CONN ACK message (acknowledge) to the network 3. In this manner, both terminals 1, 2 are communicated with each other, thereby enabling communication.
When the receiver of the originating terminal 1 has hung up (on hook) after communication is finished, the originating terminal 1 outputs a DISC message (request for disconnection) to the network 3. The network 3 transfers the DISC message to the terminating terminal 2. When the terminating terminal 2 receives the DISC message, it releases a call reference and sends a REL message (completion of the channel disconnection and call reference release request) to the network 3. The network 3 disconnects the channel, releases the call reference, and transfers the REL message to the originating terminal 1. When the originating terminal 1 receives the REL message, it releases the call reference and sends a REL COMP message (completion of the release of the channel and the call reference) to the network 3. When the network 3 receives the REL COMP message, it releases the channel and the call reference and supplies the REL COMP message to the terminating terminal 2, thereby ending the calling control.
Such a SET UP message and a CONN message between the user and the network includes traffic characteristics (transfer speed, etc.). FIG. 18 is an explanatory view of a SET UP message. A SET UP message is largely divided into a common portion (a) and an individual portion (b). The common portion (a) contains a protocol discriminator, the octet length of a call reference, a call reference, a SET UP message type, etc. The individual portion (b) contains various information. Various information is composed of an information element identifier IID, an octet length LG of an information element, and an information content ICT. In FIG. 18, information is composed of five information elements: 1 bearer capability information, 2 user channel information, 3 the number of the originating party, 4 the number of the terminating party and 5 incoming call logging information identification. The bearer capability information (1) includes an exchange mode (line or packet), information transfer capability (sound or digital), information transmission speed (64 Kbps, 384 Kbps, etc.).
In ISDN communication, frame relay communication or ATM communication, the originating terminal declares the traffic characteristics (transfer speed (band), average speed, peak speed, etc.) which are stationarily set in advance to the network and the terminating terminal by a SET UP message, and receives the notification on the reception of the SET UP message through a CONN message. For this reason, in the case of executing data communication having a high burst possibility, it is impossible to declare the appropriate traffic characteristics which correspond to the amount of data to the network and to communicate with the other party on the basis of the traffic characteristics. Efficient use of the network is therefore important for high-speed transfer.
As described above, according to a conventional LAN-LAN communication system, rapid band control is impossible so that efficient data transfer is also impossible.
In addition, in a conventional LAN-LAN communication system, it is impossible to declare the appropriate traffic characteristics which correspond to the amount of data to the network and to communicate with the other party on the basis of the traffic characteristics.